1. Field of the Invention
The present invention relates to dimmer control circuits, and more particularly to such circuits having touch sensitive controls.
2. The Prior Art
Control circuits for thyristor type lamp dimmers are in common use, and many of them energize a triac or other thyristor by means of signals developed from an integrated circuit. One such integrated circuit (or IC) is Model No. S566B, which is commercially available from the Siemens Corporation, and incorporates an MOS circuit for controlling a triac dimmer circuit. The DC power for operating the integrated circuit is derived from the line voltage, which is coupled to a load by the triac. The integrated circuit Model S566B may be controlled with two different types of touch control circuits. In one type of control circuit, a touch sensor is connected by high impedance to one input of the IC. Because of the high impedance of the circuit, the touch sensor must be located quite close to the IC, in order to avoid faulty operation due to transient noise. The other type of control circuit incorporates a transistor having its emitter and collector terminals connected in series between one side of the AC power line and another input of the IC, with a touch sensor connected between the base of such transistor and ground. Since the emitter and collector terminals of the transistor constitute a low impedance circuit, the transistor and touch sensor may be located remotely from the IC, without adverse effects. However, the touch sensor must remain located relatively close to the transistor, because of the high impedance touch sensor circuit. It is, therefore, not possible in either version of control circuit to have the touch sensor located remotely from all of the other equipment, without being subject to transient electrical noise.
Another disadvantage of the previously known touch control circuit arrangements is that proper operation of the control circuit depends upon a specific polarity of the line circuit, and if the line plug is inserted incorrectly into its receptacle, the control circuit does not function.